Glass half-full: Castle Rock could need as much as $425 million to secure water for the next generation as South Metro booms.

• Author: Best, Allen

The elevation of Castle Rock Towh Hall is 6,202, hardly an impressive figure in a state where the average mean elevation is 6,600. But from the office of utility director Ron Redd that elevation is crucial.

Read is responsible for ensuring the water supply for the city, population 42,000--up from 18,000 just seven years ago.

Located near the headwaters of Plum Creek, there's little upstream for Castle Rock or, for that matter, most other communities in Denver's South Metro area. Given that unyielding reality, Redd's fundamental task is to defy gravity. Water must be made to flow uphill.

As the old saying goes, water flows uphill to money, and Redd figures he'll ultimately need $425 million to draw the volume of water he believes will be necessary when Castle Rock reaches its assumed build-out population of 104,000. At the double-digit growth of recent years, that's likely to happen by 2030.

Ensuring water for this many people doesn't keep Redd awake.

"I sleep fine at night," he says. "There are a lot of things that will happen in the next year that will march us forward. But I'm a little nervous until they happen. I think it's my nature. I can't stop thinking about this stuff, and when I go on vacation, I need about two weeks, because for the first week I can't get it out of my head."

There is a lot to think about--and, according to some geologists, plenty that should make Redd nervous. Some 92 percent of Castle Rock's water currently comes from the aquifers that underlie the town for several thousand feet. They are finite.

Whether the underground aquifers hold enough water to last even several decades remains the nagging, unanswered question, not only in Castle Rock but across Denver's well-dependent South Metro area. The answer is ultimately unknown and, in the short term, perhaps unknowable. "It's dark down there," one geologist is fond of saying.

Castle Rock's response is what amounts to an educated gamble. The town plan is to transition to a dependency on renewable water supplies, which is to say rivers carrying snow-melt from the Rocky Mountains. Redd assumes the town has at least 30 years, maybe more. Redd's gamble is to delay the transition to renewable supplies until Castle Rock is bigger, to spread out the cost across a larger population, but without waiting too long.

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"We're 40 percent built-out now, and it's hard to ask existing residents to pay for solving the problem," he says. "There are a lot of ideas out there if money were no issue. But in reality, we're limited. This community has many needs. If there is a way to spread out the cost, that seems like the best approach."

Piggy-backing on the initiative of others in the South Metro area, Castle Rock could begin this transition to renewable water supplies in another year or two and, given the urgency of other water-providers, complete them in 15 to 20 years. The process, Redd says, is accelerating.

Critics say it's about time.

Water in these aquifers was deposited 30,000 years ago, during the last glacial advance. They are contained in what is called the Denver Formation, a region extending from Colorado Springs to Greeley, and from the foothills to about Limon. These aquifers are not great caverns, or even water-logged sand, as might be found on a beach--although some began as riverside beaches.

Now compressed into rocks, these sands and gravel retain tiny, microscopic spaces, called pores, and cracks. The more coarse the materials in these sedimentary rocks, the larger the gaps, and hence the more water they will hold. For the South Metro communities, the workhorse has been the Arapahoe Aquifer, created from gravel beds along rivers as the Rocky Mountains arose 67 million years ago. The Arapahoe provides nearly half of the water for Castle Rock.

It's a wonderful thing, this water from 2,000 feet underground. It's untainted by pollution and efficiently stored, unlike the above-ground reservoirs that lose several feet of surface each year to evaporation. Also unlike above-ground sources, the aquifers are dependable even when Dillon Reservoir is mostly mud flats.

But reservoirs eventually refill after heavy winter snows. These underground reservoirs will not last--neither in current quantities nor at current costs of extraction. In Castle Rock, the cost of electricity this year for pumping the city's wells is projected to be $2.5 million. The six newest among Castle Rock's existing 32 wells cost $10 million to drill and outfit.

"It's an expensive system," Redd says.

Diminished aquifers will require more wells, and likely deeper wells, just to produce the same amount of water. By one...